When I read they filmed an episode in Japan, I immediately thought of the Japan episode in Full House you mentioned. It was called "Road to Tokyo". Fuller House had already many connections to Full House episodes. So I think they might do a remake of "Road to Tokyo". Maybe we meet Jesse's assistent Koji again.

"Darkness cannot drive out darkness: only light can do that.
Hate cannot drive out hate: only love can do that."

The Tanners and such don't have family, but - if the writers thought this far back - the Gibblers could.

Admittedly, this is more true in Brazil and Peru, but South America has had quite a few Japanese immigrants and there are a fair number of people with Japanese ancestry there. It would also allow them to add yet another last name to Fernando's already long name, which would be funny. Ramona would then had some japanese blood, and who knows where Kimmy's family is from.